Organic light emitting diode (OLED) display devices utilize a current passed through thin film layers of organic materials to generate light. Electrodes located on either side of the organic layers provide current to the organic layers. The color of the light depends on the specific organic material and the light is emitted in every direction. A portion of the light is emitted directly toward the front of the display device: through a substrate (for a bottom emitter device) or a protective cover (for a top emitter device). A similar portion of the light is emitted toward the back of the display device and may be either absorbed or reflected by a layer behind the organic layers. OLED display devices can use emitters of different colors (for example, red, green, and blue) to form a full color display or can use color filters, either with the different colored emitters (as trimming filters), or with a single broad spectrum light emitter (for example, white) to form a full color display. The use of a white emitter with color filters to form a full color display is well known in the display industry and is practiced for liquid crystal displays and has been suggested for use with OLED displays.
The individual light emitting elements of a flat panel display are controlled by electrodes located on either side of a light emitting layer (e.g. an OLED) or a light modulating layer (e.g. an LCD). For example, OLED devices utilize a stack of organic layers (for example, hole injection, hole transport, emissive, electron transport, and electron injection layers) that, when current is passed through the layers, emit light whose frequency depends on the composition and structure of the layers and any intervening color filters. Alternatively, liquid crystal display light modulators controlled by electrodes and color filters to provide a color display. In either case, light travels through one or more of the electrodes. Hence, there is a need for transparent electrodes for flat panel displays of these types.
Transparent electrodes are known in the prior art and typically include indium tin oxide (ITO) or thin layers of various types of metals or metal alloys. These electrodes have a limited transparency and conductivity and there is a recognized need for transparent conductors having improved transparency and conductivity. One technology proposed for providing transparent conductors are carbon nanotubes arranged in a thin layer. For example, WO2002076724 A1 entitled “Coatings Containing Carbon Nanotubes” published 20021003 discloses electrically conductive films containing nanotubes. The disclosed films demonstrate excellent conductivity and transparency. Methods of preparing and using the films are disclosed.
U.S. Pat. No. 6,436,591 issued Aug. 20, 2002 to Ohtsu et al. shows a method of making a conductive color filter for an LCD display using a photoconductor and an electro deposition technique. The technique is complex and therefore expensive to implement.
There is a need therefore for an improved conductive color filter and method of making it.